Influence of different luting agents on the stress distributions of implant-supported all-ceramic single crown

The purpose of this study was to investigate the influence of different luting agents on the stress distribution within the crown, abutment and peri-implant bone of implant-supported all-ceramic single crown. A three-dimensional finite element model of an implant-supported single crown for the first premolar of mandible was created by COSMOS 2.85. Resin-modified glass ionomer and two different resin adhesives were used to cement the crown and abutment. Vertical 600 N and horizontal 225 N loads were applied to stimulate the condition of chewing. The stress distributions within the all-ceramic crown, abutment and peri-implant bone were analyzed. The experimental results show that the stress distributions of all-ceramic crown, abutment, implant and peri-implant bone were similar when different luting agents were used. The result of present study indicated that luting agents had no influence on the stress distributions of implant-supported all-ceramic single crown.     

Comparison of stress distribution of platform-switched and non-platform switched abutment for implant supported single crown

The influence of platform-switched abutment on stress distribution within the surrounding bone,fixture,abutment,and screw under various loading conditions were studied.Two 3-D finite element models representative of an implant-supported metal crown for the mandibular first molar and its surrounding bone were computed.Model A simulated the implant with non-platform-switched abutment and model B was for platform-switched abutment.A load of 100 N was applied vertically and obliquely at the center fossa,the tip of the buccal cusp and the distal fossa,respectively.The results show that the distribution of Von Mises stress in the two models is similar.When platform-switched abutment is used,the maximum Von Mises stress within the surrounding bone is lower;however,this value is higher within the fixture and screw.     

集料水平向分布状态对沥青混合料劈裂试验影响数值模拟

为研究集料水平向分布状态对沥青混合料劈裂试验的影响,基于沥青混合料集料均匀性指标,通过在混合料水平截面不同方向上加载,采用有限元法数值模拟集料水平向分布状态对沥青混合料劈裂试验中最大应力值(平面主应力和水平拉应力)的影响,并加以试验验证。研究结果表明:集料水平向分布状态对沥青混合料劈裂试验中平均最大应力值影响不大,其间相关性不明显,但与最大应力值变异性间相关性却很显著。     

Design and development of SiC/(W,Ti)C gradient ceramic nozzle

The idea of functionally gradient material (FGM) theory was used to design ceramic nozzle based on the erosion wear behaviors of the ceramic nozzles and the outstanding properties of FGM. The purpose is to reduce the tensile stress at the entry region of the nozzle during sand blasting processes. The design theory and methods of gradient ceramic nozzle were proposed. The physical, micromechanical, and composition distribution models of gradient ceramic nozzle were established. The optimum composition distribution of the gradient ceramic nozzle material was determined from the solution of the multi-objective optimization calculation by constructing the models of the composition distribution versus the structural integrity of the compact in fabricating process. Results showed that compressive residual stresses appeared at the entry area of the gradient ceramic nozzle. The optimized component distribution exponent p is 0.5. An SiC/(W,Ti)C gradient ceramic nozzle material was synthesized by hot-pressing according to the design result. Results showed that the surface Vickers hardness of the FGM-1 gradient ceramic nozzle materials was greatly improved in comparison with that of the other layers. Supported by the Specialized Research Fund for Doctoral Program of Higher Education (Grant No. 20030422105), the Natural Science Foundation of Shandong Province (Grant Nos. Y2004F08, Z2003F01) and the Program for New Century Excellent Talents in University (Grant No. NCET-04-0622)     

在水平荷载下整体式桥台桥梁受力分析

目的为找出在升温温差和降温温差下桥台桩柱内实测应力的分布和变化规律,分析水平荷载作用下整体式桥台桥梁的受力性能．方法以富裕工业园跨线桥为工程背景,以试验桥的左侧桥台作为试验对象,采用计算精度高的P-y曲线法对整体式桥台桥梁在制动力作用下的受力进行分析．结果通过与试验桥桥台桩柱内应力试验实测值的对比分析所得出P—y曲线法计算桩土相互作用的精度高于“m”法．试验桥的单侧桥台在制动力作用下的受力与在均匀温差作用下的受力具有相似性．结论采用P-y曲线法分析在水平荷载下整体式桥台桥梁的受力特性具有较高的可行性．     

水泥混凝土桥面铺装力学行为数值分析

为了分析桥面铺装层的力学特性及其影响因素,结合桥面铺装的结构形式建立了有限元模型,分析了不同水平制动力系数、铺装上下面层材料模量组合及铺装层厚度变化对铺装层内力学状态的影响规律．结果表明,不同的水平载荷对铺装层内的主应力影响较小,而对铺装层内的剪应力影响较大;随着水平载荷的增加,铺装层及防水粘接层内的最大剪应力呈线性增大的趋势;随着铺装层组合模量的提高,铺装层内的主应力变化较小,而层间剪应力相应减小,但变化的幅度较小;增加铺装层的厚度对主应力的影响很小,随着厚度的增加层间最大剪应力减小．研究结果可为桥面铺装材料的选择和结构设计提供理论参考．     

Stress spatial evolution law and rockburst danger induced by coal mining in fault zone

In order to explore the influence of coal mining disturbance on the rockburst occurring in fault zone, this research constructed a mechanical model for the evolution of fault stress, and analyzed the influence of the ratio of horizontal stress to vertical stress on the stability of fault, and the spatial distribution of the stress in fault zone as well as its evolution rule. Furthermore, the rockburst danger at different spatial areas of fault zone was predicated. Results show that: when both sides of the working face are mined out, the fault zone in the working face presents greater horizontal and vertical stresses at its boundaries but exhibits smaller stresses in its middle section; however, the ratio of horizontal stress to vertical stress is found to be greater at middle section and smaller at boundaries. As the working face advances towards the fault, the horizontal and vertical stresses of the fault firstly increases and then decreases; conversely,the ratio of horizontal stress to vertical stress keeps decreasing all the time. Therefore, if the fault zones are closer to the goaf and the coal wall, the stress ratio will be smaller, and the fault slip will be more prone to occur, therefore rockburst danger will be greater. This research results provide guidance for the rockburst prevention and hazard control of the coal mining in fault zone.     

Effect of roller shapes on strip buckling in a continuous annealing furnace

The effect of roller shapes on strip buckling in a continuous annealing furnace was focused on. The tensile stress distribution, the transverse compressive stress, and the critical buckling stress of the strip were studied by the finite element method (FEM) when the flat roller, crown roller, single taper roller, and double taper roller were used, respectively. Simulation results show that strip buckling is most likely to occur with the crown roller, then the double taper roller, and finally the single tape...     

隐伏溶洞对隧道围岩稳定性影响规律及处治技术

以鄂西山区隧道工程实例为依托,在溶洞调查与统计分析的基础上,从岩溶的溶洞体积、形态特征、溶腔充填物特征以及涌水通道类型等方面,对鄂西山区岩溶进行分类,得到鄂西山区岩溶发育特征,即溶腔体积不等、形态多样、溶腔充填物种类多、涌水通道复杂。采用数值模拟方法,分析不同位置的隐伏溶洞对隧道围岩的应力场、位移场影响情况,得出随隐伏岩溶位置变化,围岩应力分布有所不同;溶洞位置由隧道顶部向隧道底部变化过程中,隧道顶部围岩最大沉降由大到小依次为拱肩延长线、边墙一侧、拱脚延长线、拱顶上方、底板下方;随着溶洞位置的降低,隧道拱顶围岩水平最大收敛值由大到小依次为拱肩延长线、拱顶上方、边墙一侧、底板下方、拱脚延长线;随着溶洞位置的降低,隧道周边围岩沉降量由大到小均为拱顶、拱腰、拱脚、底板。基于岩溶类型特征、数值模拟围岩应力场、位移变化情况结果,提出岩溶区隧道揭露溶洞处治原则。以花果山隧道为例,开展溶洞处治原则与方法应用,提出针对性的处治方案。     

大断面软弱围岩隧道洞口段施工工法比较分析

山岭隧道建设条件复杂,通常洞口段埋深较浅、围岩破碎,在施工过程中易发生坍塌、边仰坡失稳等事故．根据某隧道洞口段地质情况、地形条件以及设计参数,对拟采用的交叉中隔壁法和双侧壁导坑法进行施工和数值分析对比．研究结果表明：从施工上看,采用交叉中隔壁法有利于工期;从数值分析看,采用交叉中隔壁法和双侧壁导坑法完成开挖后,隧道结构y向最大沉降分别为6．65cm和1．68cm,临时支撑X向最大变形分别为20．5cm和4．42cm,采用后者施工变形更小;从计算结果看,采用双侧壁导坑法施工,围岩和隧道支护结构受力更小．采用交叉中隔壁法施工后,C25喷射混凝土Y向最大拉应力为3．07MPa,远大于采用双侧壁导坑法的1．27MPa,且超过该喷射混凝土的极限抗拉强度．因此,从隧道变形和受力分析看,采用双侧壁导坑法施工更安全．     

Measurements of in situ stress and mining-induced stress in Beiminghe Iron Mine of China

In order to obtain the distribution rules of in situ stress and mining-induced stress of Beiminghe Iron Mine, the stress relief method by overcoring was used to measure the in situ stress, and the MC type bore-hole stress gauge was adopted to measure the mining-induced stress. In the in situ stress measuring, the technique of improved hollow inclusion cells was adopted, which can realize complete temperature compensation. Based on the measuring results, the distribution model of in situ stress was established and analyzed. The in situ stress measuring result shows that the maximum horizontal stress is 1.75–2.45 times of vertical stress and almost 1.83 times of the minimum horizontal stress in this mineral field. And the mining-induced stress measuring result shows that, according to the magnitude of front abutment pressure the stress region can be separated into stress-relaxed area, stress-concentrated area and initial stress area. At the −50 m mining level of this mine, the range of stress-relaxed area is 0–3 m before mining face; the range of stress-concentrated area is 3–55 m before mining face, and the maximum mining-induced stress is 16.5–17.5 MPa, which is 15–20 m from the mining face. The coefficient of stress concentration is 1.85. Foundation item: Projects(10702072, 10632100) supported by the National Nature Science Foundation of China     

聚氨酯陶瓷复合材料浆体磨损性能研究

用聚四氢呋喃醚二醇与甲苯二异氰酸酯反应后,分别与Si3N4陶瓷粉、TiO2陶瓷粉末进行共混,制得耐磨蚀聚氨酯/Si3N4和聚氨酯/TiO2陶瓷复合材料,评价了这两种材料的耐磨性,通过扫描电镜观察了复合材料的磨损形貌,探讨了Si3N4和TiO2陶瓷粉末增强聚氨酯弹性体的磨损机理。结果表明:Si3N4粉末在质量分数为10%时,复合材料的耐磨性最好,是2Cr13钢的7.8倍,是45#钢的12.5倍,是纯聚氨酯的1.87倍。当TiO2陶瓷粉末在质量分数为8%时,复合材料的耐磨性最好,聚氨酯/TiO2陶瓷复合材料的抗冲蚀磨损性能分别是2Cr13钢的5.3倍,是45号钢的8.5倍,是纯聚氨酯的1.28倍。陶瓷粉末的加入有效提高了材料的抗冲蚀磨损性。     

A case study of the stability of a non-typical bleeder entry system at a U.S. longwall mine

Longwall abutment loads are influenced by several factors, including depth of cover, pillar sizes, panel dimensions, geological setting, mining height, proximity to gob, intersection type, and size of the gob.How does proximity to the gob affect pillar loading and entry condition? Does the gob influence depend on whether the abutment load is a forward, side, or rear loading? Do non-typical bleeder entry systems follow the traditional front and side abutment loading and extent concepts? If not, will an improved understanding of the combined abutment extent warrant a change in pillar design or standing support in bleeder entries? This paper details observations made in the non-typical bleeder entries of a moderate depth longwall panel—specifically, data collected from borehole pressure cells and roof extensometers,observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading experienced due to the extraction of the longwall panels. Due to the layout of the longwall panels and bleeder entries, the borehole pressure cells(BPCs) and roof extensometers did not show much change due to the advancing of the first longwall. However, they did show a noticeable increase due to the second longwall advancement, with a maximum of about 4 MPa of pressure increase and 5 mm of roof deformation. The observations of the conditions showed little to no change from before the first longwall panel extraction began to when the second longwall panel had been advanced more than 915 m. Localized pillar spalling was observed on the corners of the pillars closest to the longwall gob as well as an increase in water in the entries. In addition to the observations and instrumentation, numerical modeling was performed to validate modeling procedures against the monitoring results and evaluate the bleeder design.ITASCA Consulting Group's FLAC3 D numerical modeling software was used to evaluate the bleeder entries. The results of the models indicated only a minor increase in load during the extraction of the longwall panels. These models showed a much greater increase in stress due to the development of the gateroad and bleeder entries--about 80% development and 20% longwall extraction. The FLAC3 D model showed very good correlation between modeled and expected gateroad loading during panel extraction. The front and side abutment extent modeled was very similar to observations from this and previous panels.     

连退炉导向辊热凸度对辊形及带钢应力分布的影响

为了更有效地控制连退炉内导向辊热凸度和改善带钢的跑偏及瓢曲变形,以单锥度辊为研究对象,运用MARC有限元软件,定量计算了在加热段和快冷段不同导向辊温差时的导向辊热凸度及其对导向辊辊形和带钢应力分布的影响.研究发现：导向辊热凸度随导向辊温差增大呈直线上升的趋势.在加热段,随着导向辊温差的增大,导向辊产生热凸度后的形状分别为双锥度辊、单锥度辊和“M”型辊,带钢张应力和带钢最大应力分布随着导向辊温差的增大而改变;在快冷段,导向辊产生热凸度后变为双锥度辊,导向辊热凸度会影响带钢张应力值和最大应力值,但不影响其分布.     

加固顶板控制巷道底鼓的数值分析

利用数值计算方法，研究了顶板强度对回采巷道围岩应力分布、塑性区范围及底鼓的影响，结果表明：巷道顶板强度提高后，巷旁支承压力峰值将向巷帮深部移动，顶板中的水平应力增加，巷道底板的塑性区范围明显减小，巷道底鼓量也将减小。在此基础上，提出了加固巷道顶板控制底鼓的观点。     

拱坝双支传力墩的设计研究

本文结合三汇拱坝,采用平面弹塑性非线性有限元程序,对坝肩双支传力墩进行了详细的计算研究。计算结果表明,拱坝坝肩节理岩体中设置双支传力墩,能有效地减小坝肩水平位移,改善岩体中的应力分布状况,并增加拱坝拱座的稳定性.     

超低温下层合板复合材料的短梁法层间剪切强度研究

采用三维有限元法对超低温下玻璃纤维强化树脂层合板的短梁法层间剪切强度进行了研究,通过与二维有限元解析结果的对比,分析了试验片三维形状对中性面上剪切应力分布的影响;通过三维有限元解析,阐明 了剪切领域内的剪切应力分布。数值解析结果表明,短梁剪切试验片的最大剪切应力并非在中性面上产生,靠近载荷点及支点附近产生较大的局部剪切应力;中性面上的剪切应力分布不均匀,但中性面上最大剪切应力均匀分布的范围较大;基于梁理论的表观层间剪切强度较中性面上的最大剪切应力值低,采用短梁剪切试验法时会产生较小的强度评价。     

考虑颗粒破碎的堆石料动力变形特性模拟

颗粒破碎是影响堆石料强度和变形特性的重要因素,但目前针对颗粒破碎的模拟研究多在静力荷载条件下.为研究颗粒破碎对小应变条件下堆石料的动力变形特性的影响,采用多个等粒径小球按最密六方排列随机组合模拟不规则形状的堆石颗粒,通过碎片替换法模拟颗粒破碎,研究了花岗岩堆石料不同围压下的动力响应,探索了孔隙率对动弹性模量的影响,分析...     

磁弹噪讯技术无损检测铁磁材料疲劳损伤

铁磁材料加工制造的机械构件，在服役的过程中，受外力作用、在其内部会产生应力集中与松驰，引起构件局部或全部的扭曲、变形，造成构件的疲劳，使设备运行不安全或破损，对铁磁构件内部应力和疲劳寿命检测一直是人们重视的检测难题。从工程应用的角度，迫切需要一种既能检测构件应力大小，分布以及构件的疲劳，而不需要通过测量应变而测应力，并能瞬间、定点、在线的检测方法，铁磁构件在交变磁场的作用下，磁畴壁的不连续运动在其表面释放一种磁弹波--巴克毫森噪讯。该巴氏噪讯对材料所受外加载荷及材料的微观结构的变化十分敏感。采用该技术可开展在线无损检测铁磁构件服役应力及疲劳损伤。本文介绍该技术的原理及对平板构件疲劳损伤无损检测的实验结果。